Even if you're fully decked out in reflective coating, riding a bike at night can be a dangerous thing, which is why Instructable user NEIN decided to rig up a simple system to add blinking turn signals to his bicycle.
It's a bit of a process to outfit the bike, but it's an inexpensive fix considering you'll end up with a safe means of transport. Using commercially available parts, NEIN hooked up a simple on/off stitch to a pair of flashing safety lights so he could easily signal to drivers behind him without using the hand signals many drivers don't recognize. Hit up the full Instructable for the instructions on how to make these yourself.
Simple turn signals for a bicycle | Instructables